<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <form action="/login" method="post" name="loginForm">
        <div>
            <label for="phoneInput"></label>
            <input type="text" name="phone" id="phoneInput"
             placeholder="请输入手机" required pattern="/^[0-9]{11}$/">
        </div>
        <div>
            <button type="submit">提交</button>
        </div>
    </form>
    <script>
        const oForm=document.forms['loginForm'];
        oForm.addEventListener('submit',function(event){
            event.preventDefault();
            const phone=oForm['phone'].value.trim();
            // console.log(phone);
            // 为空的化
            // required pattern html5 input 才有的属性
            if(!phone.length){
                alert("手机号不能为空");
                return 
            }
            if(!/^[0-9]{11}$/.test(phone)){
                alert("手机号格式有误");
            };
            this.submit();
        })
    </script>
</body>
</html>